Laser distance measuring device

ABSTRACT

The invention is based on a laser range finder that has a transmitter unit ( 10 ) with at least one laser, a receiver unit ( 12 ), and a single sideband modulation unit ( 14 ) that can use a first single sideband modulation frequency (ZF 1 ) generated by an oscillator unit ( 16 ) and a carrier frequency (T 1 ) to generate a modulation frequency (S 1 ) of the transmitter unit ( 10 ).  
     According to the invention, the oscillator unit ( 16 ) can generate at least one additional frequency (ZF 2 ) and the single sideband modulation unit ( 14 ) can use the additional frequency (ZF 2 ) to generate a demodulation frequency (S 2 ) of the receiver unit ( 12 ).

PRIOR ART

[0001] The invention is based on a laser range finder according to thepreamble to claim 1.

[0002] There are known laser range finders, which have a transmitterunit with a laser, a receiver unit, and a single sideband modulationunit. In these laser range finders, the single sideband modulation unitcan use a single sideband modulation frequency generated by anoscillator unit, which simultaneously corresponds to a low frequency ora useful signal for phase determination, and a carrier frequency togenerate a modulation frequency of the transmitter unit.

[0003] The original carrier frequency is used as a demodulationfrequency of the receiver unit.

ADVANTAGES OF THE INVENTION

[0004] The invention is based on a laser range finder that has atransmitter unit with at least one laser, a receiver unit, and a singlesideband modulation unit that can use a first single sideband modulationfrequency generated by an oscillator unit and a carrier frequency togenerate a modulation frequency of the transmitter unit.

[0005] According to the invention, the oscillator unit can generate atleast one additional frequency and the single sideband modulation unitcan use the additional frequency to generate a demodulation frequency ofthe receiver unit. A distance between the carrier frequency, themodulation frequency, and the demodulation frequency can be selectedindependent of a useful signal; in particular, this distance can beselected to be greater than the useful signal. Disturbance variables canbe easily eliminated or filtered out, particularly if the oscillatorunit can generate at least one second single sideband modulationfrequency, and the single sideband modulation unit can use the secondsingle sideband modulation frequency to generate a demodulationfrequency of the receiver unit. An inexpensive laser range finder canachieve high-precision measuring results. In lieu of using a secondsingle sideband modulation frequency, it is also possible to generatethe demodulation frequency using a second carrier frequency.

[0006] If the oscillator unit has a single high-precision oscillatorthat can generate at least the two single sideband modulationfrequencies and/or if the oscillator unit is coupled to at least twodividers with different factors that can be used to generate the singlesideband modulation frequencies, then this makes it possible to produceespecially compact, inexpensive, and lightweight laser range finders.

[0007] If the oscillator unit has at least one LF generator or lowfrequency generator and if at least one single sideband modulationfrequency can be generated by means of a synthetic frequency shifting,then a high degree of flexibility can be achieved in the frequencygeneration.

[0008] In another embodiment according to the invention, the oscillatorunit has a PLL unit or phase-locked loop unit for generating the carrierfrequency, which allows this frequency to be generated with aninexpensive circuit. However, it is also possible that an oscillatorunit with at least two PLL units can be used to generate at least twocarrier frequencies.

[0009] In another embodiment according to the invention, the oscillatorunit and the single sideband modulation unit can generate a sinusoidalsignal. However, other signal forms deemed useful by one skilled in theart are also conceivable. Sinusoidal signals, though, allow the numberof filters to be easily reduced or completely eliminated. This allowssavings in additional components, space, weight, assembly difficulty,and costs.

[0010] Although the embodiment according to the invention is in factsuitable for all laser range finders deemed appropriate by one skilledin the art, it is particularly suitable for handheld laser rangefinders, which the embodiment according to the invention permits to bedesigned not only with a high degree of measuring precision, but also ina reasonably priced, compact form.

[0011] Other advantages ensue from the following description of thedrawings. The drawings show an exemplary embodiment of the invention.The drawings, the specification, and the claims contain numerousfeatures in combination. One skilled in the art will also suitablyconsider the features individually and unite them into other meaningfulcombinations.

[0012]FIG. 1 shows a handheld laser range finder in a three-quarter viewfrom above,

[0013]FIG. 2 shows a schematically depicted circuit design of the laserrange finder from FIG. 1, and

[0014]FIG. 3 shows a schematic depiction of a spectrum of the laserrange finder from FIG. 1.

DESCRIPTION OF THE EXEMPLARY EMBODIMENT

[0015]FIG. 1 shows a laser range finder with a transmitter unit 10 fortransmitting a laser measurement signal disposed in the housing 30(FIGS. 1 and 2). The transmitter unit 10 has a laser diode, not shown,and a collimation lens, which can be used to direct the measurementsignal in a bundled form through an outlet conduit.

[0016] The laser range finder also has a receiver unit 12 with a lens,not shown, which captures measurement signal components reflectedagainst an object and directs them to an optoelectronic converter. Theconverter, which is preferably embodied as an avalanche photodiode,receives the measurement signal components and conveys them inelectrical form to a computing unit or evaluation unit that is likewisenot shown.

[0017] The top 32 of the laser range finder is provided with a displayunit 34 and a number of push buttons 36 (FIG. 1).

[0018] The laser range finder also has a single sideband modulationfrequency unit 14 that can use a single sideband modulation frequencyZF1 generated by an oscillator unit 16 and a carrier frequency T1 togenerate a modulation frequency S1 of the transmitter unit 10 (FIGS. 2and 3).

[0019] According to the invention, the oscillator unit 16 can generate asecond single sideband modulation frequency ZF2; the single sidebandmodulation unit 14 can use the second single sideband modulationfrequency ZF2 to generate a demodulation frequency S2 of the receiverunit 12.

[0020] The oscillator unit 16 has a single high-precision oscillator 18that can generate the single sideband modulation frequencies ZF1, ZF2 bymeans of two dividers 20, 22 with different factors that are coupled tothe oscillator unit 16. The single sideband modulation frequency ZF1and/or ZF2 could, however, also be synthetically generated by means ofan LF generator 24, 26, as indicated in FIG. 2. In this connection, thedividers 20, 22 can be provided with the same factor.

[0021] In addition, the high-precision oscillator 18 can also generatethe carrier frequency T1 for the transmitter unit 10 and a carrierfrequency T2 for the receiver unit 12, in fact by means of a PLL unit 28of the oscillator unit 16, which has a PLL block 38 or phase-locked loopblock and a VCO block 40 or voltage-controlled oscillator block. Thecarrier frequencies T1, T2, however, could also be generated by separateoscillators.

[0022] The single sideband modulation unit 14, which has a first singlesideband modulator 42 for the transmitter unit 10 and a second singlesideband modulator 44 for the receiver unit 12, is preceded by filtersF1, F2 in the path 46 of the transmitter unit 10 and in the path 48 ofthe receiver unit 12 in order to filter out undesired frequencies fromthe single sideband modulation frequencies ZF1, ZF2, which can also bereferred to as intermediate frequencies. The oscillator unit 16 isfollowed by three filters F3, F4, F5, a central filter F3 immediatelyafter the VCO block 40, and a respective filter F4 and F5 for the path46 of the transmitter unit 10 and the path 48 of the receiver unit 12.In addition, after the single sideband modulation unit 14, thetransmitter unit 10 and the receiver unit 12 are each preceded by afilter F6, F7.

[0023] Fundamentally, the paths 46, 48 for the transmitter unit 10 andthe receiver unit 12 could also be exchanged and the frequency S2 couldbe used for modulating the transmitter unit 10 and the frequency S1could be used for demodulating the receiver unit 12.

[0024] It would also be possible for the oscillator unit 16 and thesingle sideband modulation unit 14 to generate a sinusoidal signal,which would permit the filters F1-F5 to be simply omitted. Other signalforms can require filters of different designs and combinations deemedappropriate by one skilled in the art, particularly in the paths 46, 48of the transmitter unit 10 and the receiver unit 12. The filters F1-F5serve in particular to achieve a particular measuring precision and tolimit the bandwidth.

[0025] The single sideband modulator 42 of the single sidebandmodulation unit 14 shifts the carrier frequency T1 with the singlesideband modulation frequency ZF1, which produces the modulationfrequency S1 of the transmitter unit 10 and the frequency S1′ or thesidebands S1 and S1′ as well as the carrier frequency T1*. The singlesideband modulator 44 of the single sideband modulation unit 14 shiftsthe carrier frequency T2 with the single sideband modulation frequencyZF2, which produces the demodulation frequency S2 of the receiver unit12, the frequency S2′ or the side bands S2 and S2′ as well as thecarrier frequency T1*. The carrier frequencies T1, T2 have a greateramplitude than the carrier frequencies T1*, T2*; otherwise the carrierfrequencies T1, T2, Ti*, T2* are identical. The elimination of thefilters F3 to F5, which is possible with an appropriate choice of thesignal form, would cause the carrier frequencies T1 and T2 to coincide.

[0026] The suppressed frequencies S1′, S2′ or the suppressed sidebandsare approximately 40 dB lower than the modulation frequency S1 of thetransmitter unit 10 and the demodulation frequency S2 of the receiverunit 12. The suppressed carrier frequencies T1*, T2* are also typicallyapprox. 40 dB lower than the modulation frequency S1 of the transmitterunit 10 and the demodulation frequency S2 of the receiver unit 12.

[0027] In the demodulation, all of the frequencies T1*, S1, S1′ of thefirst path 46 of the transmitter unit 10 are mixed with all of thefrequencies T2*, S2, S2′ of the path 48 of the receiver unit 12.Disturbance vectors generated as a result of this are significantlysmaller than in conventional systems (S1′ *S2′-approx. 80 dB) or are farenough removed in terms of frequency from an LF useful signal, which isproduced from a difference between the signals of the first path 46 ofthe transmitter unit 10 and the path 48 of the receiver unit 12 (in theratio of intermediate frequency to LF useful signal) that they can befiltered out with no trouble. In particular, with an appropriate choiceof the single sideband modulation frequencies ZF1, ZF2, the vectors thatare produced by multiplying the frequency S1′ by the carrier frequencyT2* and by multiplying the frequency S2′ by the carrier frequency T1*lie far above the frequency of the LF useful signal, which is producedby mixing the modulation frequency S1 and the demodulation frequency S2and in this exemplary embodiment, lies at about 4 kHz.

1. A laser range finder that has a transmitter unit (10) with at leastone laser, a receiver unit (12), and a single sideband modulation unit(14) that can use a first single sideband modulation frequency (ZF1)generated by an oscillator unit (16) and a carrier frequency (T1) togenerate a modulation frequency (S1) of the transmitter unit (10),characterized in that the oscillator unit (16) can generate at least oneadditional frequency (ZF2) and the single sideband modulation unit (14)can use the additional frequency (ZF2) to generate a demodulationfrequency (S2) of the receiver unit (12).
 2. The laser range finderaccording to claim 1, characterized in that the oscillator unit (16) cangenerate at least one second single sideband modulation frequency (ZF2),and the single sideband modulation unit (14) can use the second singlesideband modulation frequency (ZF2) to generate a demodulation frequency(S2) of the receiver unit (12).
 3. The laser range finder according toclaim 2, characterized in that the oscillator unit (16) has a singlehigh-precision oscillator (18) that can generate at least the two singlesideband modulation frequencies (ZF1, ZF2).
 4. The laser range finderaccording to claim 2 or 3, characterized in that the oscillator unit(16) is coupled to two dividers (20, 22) with different factors that canbe used to generate the single sideband modulation frequencies (ZF1,ZF2):
 5. The laser range finder according to one of claims 2 to 4,characterized in that the oscillator unit (16) has at least one LFgenerator (24, 26) and at least one single sideband modulation frequency(ZF1, ZF2) can be generated by means of a synthetic frequency shifting.6. The laser range finder according to one of the preceding claims,characterized in that the oscillator unit (16) has a PLL unit (28) forgenerating the carrier frequency (T1, T2).
 7. The laser range finderaccording to one of the preceding claims, characterized in that theoscillator unit (16) and the single sideband modulation unit (14) cangenerate a sinusoidal signal.
 8. A method for signal generation of alaser range finder that has a transmitter unit (10) and a receiver unit(12), and in which a single sideband modulation unit (14) uses a firstsingle sideband modulation frequency (ZF1) generated by an oscillatorunit (16) and a carrier frequency (T1 ) to generate a modulationfrequency (S1) of the transmitter unit (10), characterized in that theoscillator unit (16) generates at least one additional frequency (ZF2)and the single sideband modulation unit (14) uses the additionalfrequency (ZF2) to generate a demodulation frequency (S2) of thereceiver unit (12).